Speed control with stop function

ABSTRACT

Cruise control system for motor vehicles is provided, which control system has a sensor device for measuring the vehicle&#39;s performance characteristics and for measuring the distance to a target ahead of the vehicle, a controller to control the vehicle&#39;s speed or acceleration as a function of the measured performance characteristics and distance data, and an input device for a shut-off command to shut off the controller. The control system also has a shut-off function to shut off the controller as a function of other operational commands from the driver, and the controller has a stop function for automatically braking the vehicle to a standstill. The input device for the shut-off command is deactivated if the stop function is active and the vehicle is stationary.

FIELD OF THE INVENTION

The present invention relates to a cruise control system for motorvehicles, which system has a sensor device to measure the vehicle'sperformance characteristics and to measure the distance to a targetlocated in front of the vehicle, a controller to control the vehicle'sspeed or acceleration as a function of the measured performancecharacteristics and distance data, and an input device for a shut-offcommand to shut off the controller, as well as having a shut-offfunction to shut off the controller as a function of other operationalcommands from the driver.

BACKGROUND INFORMATION

A cruise control system makes it possible to set the vehicle's speed toa desired level selected by the driver. If the sensor device for thevehicle incorporates a distance sensor, for example in the form of aradar sensor, a stereo camera system or the like, the vehicle speed canalso be set in such a way that a suitable safety distance to a vehicleahead is automatically maintained. The input device for the shut-offcommand, which may, for example, take the form of a control button onthe steering wheel or dashboard, allows the driver to deactivate variouscontrol functions. Other operational commands from the driver, e.g.,pressing the brake pedal, have the effect of deactivating the controlfunctions.

An example of a cruise control system, which is also known as an ACC(Adaptive Cruise Control) system, is described in “Adaptive CruiseControl Systems—Aspects and Development Trends,” by Winner, Witte, Uhlerand Lichtenberg, Robert Bosch GmbH, in SAE Technical Papers Series961010, International Congress and Exposition, Detroit, Feb. 26–29,1996. Since the available sensor devices do not yet permit completecoverage and safe evaluation of the traffic environment, at present suchsystems are primarily suitable for relatively stable traffic situations,such as driving on a highway or expressway. In urban traffic, or whendriving at low speeds on winding roads, however, the uncertainties indetecting the particular relevant target object could create a risk ofaccident. For this reason, known ACC systems are designed in such a waythat they can be activated only above a certain threshold speed.

Some systems attempt to expand the range of application of the ACCsystem to the traffic situation described as “stop-and-go,” whichoccurs, for example, in a traffic jam or in slow-moving traffic. Thistraffic situation, too, is relatively stable and is therefore suitablefor automatic distance control. However, the functionality has to beexpanded in such way that stopping and preferably also starting may becontrolled automatically. On vehicles having automatic transmission,this may be achieved by means of accelerator and brake control signals,which have the same effect as the driver's pressing the acceleratorpedal or brake pedal. However, it must be ensured that road safety isnot jeopardized by vehicle responses which the driver is not expecting.

An object of the present invention is to provide a cruise control systemwhich makes it possible to automatically brake the vehicle to astandstill and to hold the vehicle in stationary position withoutjeopardizing road safety.

SUMMARY

The above object is achieved according to the present invention througha controller having a stop function for automatic braking of the vehicleto a standstill and through an input device for inputting a shut-offcommand, which input device is deactivated while the stop function isactive and the vehicle is stationary.

In a traffic jam, the driver may activate the stop function so that thecontrolled vehicle is automatically braked to a standstill as soon asthe vehicle immediately ahead of it stops. In this process, thecontroller automatically applies the vehicle's brake and keeps itapplied so that the vehicle does not begin to roll after coming to ahalt. Thus, in contrast with conventional vehicles having automatictransmissions, the driver does not need to keep a foot on the brakepedal. This results in a great increase in convenience and in roadsafety.

However, in the absence of additional safety precautions, in thissituation there would be a risk that the driver might shut off thecruise control system by simply pressing a button, without consideringthat the brake would then no longer be automatically applied and thatthe vehicle would unintentionally begin to roll. This risk is avoidedaccording to the present invention by the feature that the input devicefor the shut-off command is automatically rendered ineffective wheneverthe stop function is active and the vehicle is stationary. At astandstill, then, the stop function may only be deactivated by adifferent operational command from the driver, such as pressing thebrake pedal, setting the hand brake or placing the selector lever of theautomatic transmission in Neutral or Park.

It is advantageous if the controller not only implements a stopfunction, but also a stop-and-go function which in stop-and-go trafficautomatically controls not only stopping but also restarting and slowforward rolling of the vehicle as a function of the distance to thetarget. The operational commands which activate the stop function or thestop-and-go function when the vehicle is at a standstill may alsoinclude the action of the driver pressing the accelerator. Normally,with an ACC system, pressing the accelerator does not automatically shutoff the cruise control but only temporarily overrides it. When thedriver releases the accelerator again, cruise control automaticallyresumes on the basis of the former desired speed or the former requireddistance to the vehicle ahead. Basically, this overriding action usingthe accelerator is also possible within the stop-and-go function. If,however, the driver presses the accelerator while the vehicle isstationary, it is highly likely that the driver does not wish tocontinue the stop-and-go operation but instead, for example, wishes topull rapidly out of the line of vehicles. Consequently, in thissituation it is useful to also interpret pressing of the accelerator asan operational command to shut off the stop-and-go function. This willnot jeopardize road safety, since a driver pressing the accelerator inany event expects the vehicle to start to move.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a block diagram of a cruise control system and relatedoperation and display components.

FIG. 2 shows a diagram of the speed ranges in which various functions ofthe cruise control system are usable.

FIG. 3 shows a flowchart of a program which is implemented in the cruisecontrol system according to the present invention.

DETAILED DESCRIPTION

Since the basic design and mode of operation of a cruise control systemhaving an ACC function are known, FIG. 1 shows only the major componentsof a cruise control system in a block diagram. A sensor device 10incorporates a distance sensor, e.g., a radar sensor, which measures thedistance to, and relative speed of, a vehicle ahead. If the radar sensordetects several targets, e.g., several vehicles or stationary targetssuch as road signs and the like, one target is selected, for examplethrough a plausibility assessment.

Sensor device 10 may also include sensors of a known type, for example adriving speed sensor, acceleration sensors to detect both longitudinaland transverse acceleration, a yaw rate sensor and the like, which arenormally present in the vehicle in any event and whose signals are alsoused for other control purposes. The signals from the distance sensorand the other sensors are evaluated in an electronic controller 12,which, for example, is a microcomputer. Controller 12 acts on thevehicle's propulsion and braking system in order to regulate the drivingspeed, e.g., to a desired speed selected by the driver or to a suitabledistance to the vehicle ahead. This control function, which will bereferred to below as the ACC function, is activated by the driver'spressing an ACC button 14. If a desired speed has already been stored,pressing the ACC button causes control to be resumed at that desiredspeed. If not, the desired speed is set by the driver's briefly pressinga button 16 once the vehicle has reached the desired speed. Furtherpressing of button 16, or holding it, will cause a progressive increasein the desired speed. Similarly, pressing button 18 will cause aprogressive decrease in the desired speed.

The ACC function switches off automatically as soon as the speed of thevehicle drops below a specified level V₁, for example 40 km/h. As soonas the speed drops below a higher level V₂, for example 50 km/h,however, the driver may activate a stop-and-go function by pressing abutton 20. The driver will make use of this function, for example, whenhe is approaching the end of a traffic jam. The stop-and-go functionthen causes the vehicle to be brought to a standstill automatically at asuitable distance to the end of the traffic jam. If the stopped vehicleahead drives forward for a short distance, the stop-and-go function thencauses the vehicle to start automatically and drive itself a shortdistance forward. In this process the speed of the vehicle is limitedautomatically to speed V₂, or to a lower desired speed selected by thedriver using buttons 16 and 18. It should be noted here, however, thatthe desired speed cannot be selected to be lower than V₁.

By means of a button 22 (input device for shut-off command), the ACCfunction and also the stop-and-go function may be switched off.

Buttons 14, 16, 18 and 20 may also be integrated into a multi-functionlever, which is located, for example, on the steering wheel.Alternatively or additionally, the commands may also be input by meansof a voice recognition system.

FIG. 2 illustrates the speed ranges in which the ACC function and thestop-and-go function may be activated. In the range between V₁ and V₂both functions may be activated, although they are mutually exclusive.

A lamp 24 (FIG. 1) lights up to indicate that the ACC function isactive. This lamp 24 has an intermediate status between “on” and “off.”This intermediate status may be, for example, that the lamp lights upless brightly, or changes color, or that only a segment around the lamplights up, indicating that the ACC function is ready for activation butnot active. Similarly, if lamp 26 lights up or assumes an intermediatestatus, this indicates that the stop-and-go function is active or readyfor activation. By pressing the accelerator the driver may overrideeither the ACC function or the stop-and-go function, in order toaccelerate temporarily to a higher speed. However, pressing the brakepedal, or pressing button 22, will cause the cruise control system to bedeactivated. If the driver himself has braked the vehicle to astandstill, the stop-and-go function cannot be activated from astationary condition, but only after the driver himself has set thevehicle in motion again by pressing the accelerator. Switching thestop-and-go function back on again in such a case requires that thedriver actively press button 20. As an example, it should be assumed inthe following text that the vehicle in which the cruise control systemis installed has an automatic transmission. Controller 12 may then acton the vehicle's power system by way of an accelerator control signalwhich has the same function as the driver pressing the acceleratorpedal. Similarly, intervention in the braking system results from abraking control signal that has the same effect as the driver pressingthe brake pedal. If the stop-and-go function is active and the vehicleis braked to a standstill, the accelerator control signal is initiallycancelled in order to allow the vehicle to coast to a stop, and finallythe brake control signal is output in order to bring the vehicle to acomplete standstill. When the vehicle is stationary, the brake controlsignal is maintained, so that the vehicle does not begin to roll again.

A program implemented in controller 12 periodically, for example atintervals of the order of magnitude of a few milliseconds, interrogateswhether one of buttons 14, 16, 18, 20, or 22 has been pressed or whetherthe driver has input another operational command, e.g., by pressing theaccelerator pedal or brake pedal or by moving the transmission selectorlever. FIG. 3 is a flowchart illustrating some main parts of the controlprogram according to the present invention. In particular, this programstipulates under what conditions the stop-and-go function may beswitched off. Here it should be noted that the result of switching offthe stop-and-go function when the vehicle is stationary is that thebrake control signal drops out and thus the vehicle begins to roll. Inorder to prevent a dangerous situation or an irritation for the driver,switching off of the stop-and-go function using button 22 (OFF button)is allowed only under certain conditions, as will be explained below.

The program is started in step S1 shown in FIG. 3, which programinterrogates periodically the operating commands input by the drivereither by pushing a button or by pressing a pedal. Step S2 checkswhether OFF button 22 was pressed in the preceding interrogation cycle.

If this is the case, step S3 checks whether the stop-and-go function isactive. If the stop-and-go function is not active, this means that theACC function is active. In that case the vehicle is in motion and itsspeed is at least V₁. Pressing OFF button 22 therefore means that thedriver wishes to resume control of the vehicle himself and there is nohindrance to switching off the control function.

Consequently, the program branches to step S4, and the ACC function isswitched off. The cruise control system, however, remains in a standbystate, in which commands from buttons continue to be interrogated.Provided that the vehicle speed permits this, it is possible for the ACCfunction or the stop-and-go function to be activated again by means ofbuttons 14, 20. This is indicated by the intermediate status of lamps24, 26.

If step S3 has determined that the stop-and-go function is active, stepS5 checks again whether the vehicle is stationary. Only if the vehicleis still in motion is the stop-and-go function switched off in step S4.If the vehicle is stationary, step S6 interrogates once again whetherthe driver has pressed the accelerator. By pressing the accelerator thedriver indicates that he wishes to resume control of the vehicle andthat he anticipates that it will start to move. Consequently, in thiscase the stop-and-go function is switched off in step S4. If, however,the driver has not pressed the accelerator the program jumps back fromstep S6 to step S2. This means that when the vehicle is stationary andthe accelerator is not pressed, pushing of the OFF button 22 is ignored.This prevents the vehicle from starting to roll because the driver hasunmindfully pushed the OFF button.

If step S2 has determined that OFF button 22 was not pressed, step S7investigates whether the driver has pressed the brake pedal. If thebrake pedal has been pressed, the program branches in any event to stepS4 and the control function (i.e. the ACC function or the stop-and-gofunction) is switched off.

If the driver has not pressed the brake pedal, step S8 checks whetherthe driver has set the hand brake. Setting the hand brake too causes thecontrol function to be switched off in step S4.

If the hand brake has not been set, step S9 finally checks whether thedriver has placed the selector lever of the automatic transmissioneither in Neutral (N) or in Park (P). If this is the case, there is nodanger that the vehicle will start to roll unexpectedly, and the controlfunction is switched off in step S4.

If this is not the case, steps S10, S11 and S12 follow, carrying out thesame interrogations as in steps S3, S5 and S6. If the results of theseinterrogations are negative, the program jumps back to step S2 and theinterrogation cycle is repeated. If, however, the stop-and-go functionis active, the vehicle is stationary and step S12 determined that theaccelerator was pressed, the control system is switched off in step S4.This makes it possible for the driver to set the vehicle in motion againsimply by pressing the accelerator, without having to press the OFFbutton.

The result is to ensure that with the vehicle stationary the stop-and-gofunction may be switched off only by pressing the accelerator or thebrake pedal, setting the hand brake or moving the transmission selectorlever, but not simply by pressing the OFF button 22.

In a modified exemplary embodiment, rather than checking for thevehicle's being stationary, step S5 may also interrogate for a moregeneral condition, for example the condition that the controller isoutputting the brake control signal or that the function “Brake to astandstill” has been triggered in the controller. In this case thepressing of OFF button 22 during stop-and-go operation is blocked notonly once the vehicle is actually stationary but earlier, once it isabout to come to a standstill.

1. A cruise control system for a motor vehicle, comprising: a sensordevice for measuring the vehicle's performance characteristics and thedistance to a target ahead of the vehicle; a controller for controllingat least one of the vehicle's speed and acceleration as a function ofthe measured performance characteristics and the distance to the target,wherein the controller has a stop function for automatically braking thevehicle to a standstill; and an input device for inputting a shut-offcommand to shut off the controller, wherein the shut-off function toshut off the controller is also triggered by at least one of selectedoperational commands from the driver other than an activation of theinput device, and wherein the input device for the shut-off command isdeactivated if the stop function of the controller is active and thevehicle is stationary.
 2. The cruise control system according to claim1, wherein the stop function of the controller is a part of astop-and-go function for automatic control of the vehicle's stopping andstarting as a function of the distance to the target.
 3. The cruisecontrol system according to claim 1, wherein one of the selectedoperational commands from the driver to trigger the shut-off function ispressing of a brake pedal.
 4. The cruise control system according toclaim 1, wherein one of the selected operational commands from thedriver to trigger the shut-off function is setting of a hand brake. 5.The cruise control system according to claim 1, wherein the vehicle hasan automatic transmission and an automatic-transmission selector lever,and wherein one of the selected operational commands from the driver totrigger the shut-off function is moving the automatic-transmissionselector lever to a position other than a position for driving forward.6. The cruise control system according to claim 1, wherein the stopfunction of the controller is switched off by the driver's pressing theaccelerator when the vehicle is stationary.